Method and apparatus for electroplating

Abstract

An apparatus for electroplating a layer of metal onto the surface of a wafer includes an ionically resistive ionically permeable element located in close proximity of the wafer and an auxiliary cathode located between the anode and the ionically resistive ionically permeable element. The ionically resistive ionically permeable element serves to modulate ionic current at the wafer surface. The auxiliary cathode is configured to shape the current distribution from the anode. The provided configuration effectively redistributes ionic current in the plating system allowing plating of uniform metal layers and mitigating the terminal effect.

What is claimed is: 
     
       1. An apparatus for electroplating metal onto a substrate, the apparatus comprising:
 (a) a plating chamber configured to contain an electrolyte and an anode while electroplating metal onto the substrate; 
 (b) a substrate holder configured to hold the substrate such that a plating face of the substrate is positioned at a defined distance from the anode during electroplating, the substrate holder having one or more electrical power contacts positioned around a substantially circular perimeter and arranged to contact an edge of the substrate and provide electrical current to the substrate during electroplating; 
 (c) an ionically resistive ionically permeable element shaped and positioned between the substrate and the anode during electroplating, the ionically resistive ionically permeable element having a substantially flat upper surface that is substantially parallel to and separated from a plating face of the substrate by a gap of about 5 millimeters or less during electroplating, wherein the ionically resistive ionically permeable element has an ionically resistive body with a plurality of perforations made in the body such that the perforations do not form communicating channels within the body and wherein said perforations allow for transport of ions through the element; 
 (d) a first auxiliary cathode located between the anode and the ionically resistive ionically permeable element, and peripherally oriented to shape the current distribution from the anode, while the first auxiliary cathode is supplied with current during electroplating; and 
 (e) a second auxiliary cathode positioned to be located between the ionically resistive ionically permeable element and the substrate during electroplating, wherein the second auxiliary cathode is adapted to divert a portion of ionic current from an edge region of the substrate. 
 
     
     
       2. The apparatus of  claim 1 , wherein substantially all said perforations in the body of the ionically resistive ionically permeable element have a principal dimension or a diameter of the opening on the surface of the element facing the surface of the substrate of no greater than about 5 millimeters. 
     
     
       3. The apparatus of  claim 1 , wherein the ionically resistive ionically permeable element is a disk having between about 6,000-12,000 perforations. 
     
     
       4. The apparatus of  claim 1 , wherein the ionically resistive ionically permeable element has a porosity of about 5% or less. 
     
     
       5. The apparatus of  claim 1 , wherein the second auxiliary cathode is located in substantially the same plane as the substrate, during electroplating. 
     
     
       6. The apparatus of  claim 5 , wherein the second auxiliary cathode is located peripheral to the substrate holder and radially outward of a peripheral gap between the ionically resistive ionically permeable element and the substrate holder. 
     
     
       7. The apparatus of  claim 1 , wherein the second auxiliary cathode is a virtual auxiliary cathode having an associated physical cathode housed in a cavity in the plating chamber, wherein the cavity is in ionic communication with the plating chamber. 
     
     
       8. The apparatus of  claim 1 , further comprising a second ionically resistive ionically permeable element, wherein the second ionically resistive ionically permeable element is positioned proximate the first auxiliary cathode. 
     
     
       9. The apparatus of  claim 8 , wherein the second ionically resistive ionically permeable element has an ionically resistive body with a plurality of perforations made in the body such that the perforations do not form communicating channels within the body, wherein said perforations allow for transport of ions through the element, and wherein substantially all perforations have a principal dimension or a diameter of the opening on the surface of the element facing the interior of the plating chamber of no greater than about 10 millimeters. 
     
     
       10. The apparatus of  claim 8 , wherein the second ionically resistive ionically permeable element has a porosity of about 5% or less. 
     
     
       11. The apparatus of  claim 8 , wherein the second ionically resistive ionically permeable element is less than about 25 mm thick. 
     
     
       12. The apparatus of  claim 1 , further comprising a control circuit designed or configured to control electrical power delivered to the first auxiliary cathode such that the power is delivered only in the beginning of electroplating, but not for the entire time of electroplating the substrate. 
     
     
       13. The apparatus of  claim 12 , wherein the control circuit is designed or configured to ramp down electrical power delivered to the first auxiliary cathode and the second auxiliary cathode, each at different rates, as metal is deposited on the substrate. 
     
     
       14. The apparatus of  claim 12 , wherein the control circuit is designed or configured to supply no current or substantially no current to the first auxiliary cathode after the sheet resistance of the substrate surface reaches about 1 ohm/square or less. 
     
     
       15. The apparatus of  claim 12 , wherein the control circuit is designed or configured to supply no current or substantially no current to the first auxiliary cathode after metal is plated onto the substrate for a period of about 5 seconds or less. 
     
     
       16. The apparatus of  claim 15 , wherein the control circuit is programmed with current-time instructions to supply no current or substantially no current to the first auxiliary cathode after metal is plated onto the substrate for a period of about 5 seconds or less. 
     
     
       17. The apparatus of  claim 12 , wherein the control circuit is designed or configured to supply current to the first auxiliary cathode and the substrate at a ratio of at least about 1:2 when current plating begins. 
     
     
       18. The apparatus of  claim 12 , wherein the control circuit is designed or configured to supply current to the first auxiliary cathode and the substrate at a ratio of at least about 5:1 when current plating begins. 
     
     
       19. The apparatus of  claim 1 , wherein the distance between the first auxiliary cathode and a lower surface of the ionically resistive ionically permeable element is less than about a radius of the substantially circular perimeter around which the one or more electrical power contacts are positioned.